1. Field of the Invention
This invention relates generally to a voltage converter, and more particularly is directed to an improved transformer-less DC-DC converter for boosting or changing the polarity of a supply voltage.
2. Description of the Prior Art
In order to boost a DC voltage with a DC-DC converter, it has been proposed in the prior art to provide an oscillator operated by the DC voltage, and to boost an output from the oscillator by means of a boosting transformer with the output from the boosting transformer being rectified to obtain the desired DC voltage.
In such a converter, in order to minimize the size of the boosting transformer or to enhance its boosting efficiency, the oscillator has a high frequency, such as, for example, 30 KHz. However, if the oscillation frequency of the oscillator is high and the converter is incorporated in another device, for example, a radio receiver, or used together with the latter, high harmonics of the output from the oscillator are received by the radio receiver and disturb other signals. Further, leakage magnetic flux from the boosting transformer may adversely affect other circuits.